Locked loop circuits, such as phase-locked loops, typically generate timing signals relative to an input reference signal. The locked loop circuitry adjusts the frequency of an output signal based on frequency and/or phase differences between the reference signal and the output signal. Based on any such difference, the frequency and/or phase of the output signal is increased or decreased accordingly. Phase-locked loops are used in a wide range of electronics, such as radios, telecommunication circuits, wireless and mobile devices, computers, and other devices.
Digital phase-locked loops often employ a digitally-controlled oscillator (DCO) that converts an input digital word received from a loop filter into a periodic signal output at a given frequency. Conventional DCO circuits generate the periodic output based on a multi-bit DCO codeword that acts as a function applied to the input digital word from the loop filter. Under various operating conditions, such as those involving process, voltage or temperature (PVT) variations, the DCO codeword may exhibit gain variation, consequently introducing error in the frequency and/or phase of the output signal.
Accordingly, what is needed are methods, systems and associated apparatus that allow for compensating for DCO gain variations in a straightforward, efficient and predictable manner.